The polymeric pigment dispersants of this invention are polyester/acrylic graft polymers having a cyclic imide and quaternary ammonium groups. These dispersants are useful for dispersing a wide variety of pigments.
The most useful pigment dispersants are broadly compatible with other polymers, selectively adsorbed by a wide range of pigments, soluble in a wide range of solvents, and not displaced from pigment surfaces by polar solvents. Certain pigments are particularly difficult to disperse, for example carbon black pigments, and require special dispersants that do not allow the pigments to flocculate or cause an increase in viscosity of the dispersion or resulting paint composition.
Simms et al U.S. Pat. No. 5,424,364 issued Jun. 13, 1995 shows the use of acrylic polyester comb polymers having imide groups as pigment dispersants. Yamamoto et al U.S. Pat. No. issued Feb. 16, 1993 shows acrylic polyester polymer containing amine groups that are used as pigment dispersants. European Patent Application 0 458 479 A2 published Nov. 27, 1991 shows pigment dispersants of acrylic polymers having tertiary amino groups and/or nitrogen-containing heterocyclic rings and a particular polyester component.
While these pigment dispersants are adequate, there is a need for pigment dispersants that can be readily prepared and are more effective for dispersing a wide variety of pigments in various coating compositions used in the field of high performance coatings.